The present invention relates to a method for producing an electron tube equipped with a shadow mask for TV sets or computers.
One of the conventional methods for producing an electron tube is disclosed by Japanese Patent Application Laid-Open No. 59-94325. FIG. 1 illustrates a structure of electron tube, wherein 1 is a shadow mask, 1a is the shadow mask side facing an electron gun, 2 is an electron gun, 3 is a fluorescent plane, 4 are electron beams, and 5 is an electron tube. The shadow mask made of a metallic material is provided with a number of openings, and is designed to match with the fluorescent plane. When the electron tube is switched on, the electron beams issued by the electron gun pass through the beam-transmitting openings to hit the fluorescent plane, generating desired images thereon.
Most of the electrons, however, hit the shadow mask without passing the openings, with the result that energy of motion of the electrons is transmitted as thermal energy to the shadow mask, to heat it to 70xc2x0 C. or higher. This temperature rise thermally expands the shadow mask to cause misalignment between the opening sections in the shadow mask and fluorescent plane, causing problems, e.g., color shift and lowered brightness. The problematic phenomenon of thermal expansion of the shadow mask caused by shooting electron beams is referred to as doming.
It is known that these problems are controlled by coating the shadow mask side 1a facing the electron gun with a coating material containing an element having an atomic number of 70 or more to form an electron beam reflecting film. In particular, the coating material containing powdered bismuth oxide or the like is considered to be suitable, because of its effect of efficiently reflecting the electron beams (hereinafter referred to as electron-reflecting effect). It is also known that an element having a larger atomic number shows a larger electron-reflecting effect. Therefore, the shadow mask side 1a is coated with a coating material containing a material of large electron-reflecting effect, such as powdered bismuth oxide, to reflect the electron beams that hit the shadow mask. The electron beam reflecting film is generally formed by spraying, in which the electron beam reflecting coating material is supplied by a high-capacity pump, e.g., magnet pump, to a nozzle to prevent settling of the coating material in the nozzle and piping systems, and the nozzle is scanned over the shadow mask to form the film. The electron beam reflecting film formed on the shadow mask side facing the electron gun prevents temperature rise of the shadow mask, and thereby to solve the problems, such as color shift, caused by doming.
The surface coat is formed by spreading a surface coating material, such as that containing SiO2 or ITO, to realize a low-reflection function and anti-static function by resultant difference in refractive index and its conductivity. The coating material is spread by spraying or spin coating, the latter being a normal choice, because of difficulty of the former to give a dense, homogeneous coating film.
A common method for producing the coating material for electron beam reflecting films is dispersion by a rotating device, such as a ball mill. However, the coating material dispersed by this method tends to suffer secondary agglomeration, after it is dispersion-treated, which causes problems, e.g., settlement of the coating material in, and clogging of, the coating systems, making it difficult to inject the coating material stably from the nozzle and to form a dense, homogeneous electron beam reflecting film. Another dispersion method uses a sand mill. The method using such a medium, however, has disadvantages, e.g., breakdown of the medium itself in a dispersion machine to contaminate the coating material, and unstable dispersion conditions of the coating material, because of newly evolved interfaces as a result of destruction of coating material particle shapes.
Moreover, the conventional coating material for electron beam reflecting films contains particles of large average size and unstable particle size distribution. In order to secure a high surface coverage of the electron beam reflecting film, it is necessary to spread a large quantity of the coating material over the shadow mask side, to 0.2 mg/cm2 or more, as disclosed by Japanese Patent Application Laid-Open No. 59-94325. As a result, the film tends to come off from the shadow mask in the electron tube product, causing problems, e.g., contamination within the electron tube and lowered image quality.
The method for forming an electron beam reflecting film by spraying supplies the coating material to the nozzle and recycles it by a high-capacity pump, e.g., a magnet pump. This method, however, involves problems, e.g., adverse effects of fluctuating pump discharge pressure on discharge conditions of the coating material at the nozzle, causing uneven coating as a result of fluctuations in quantities discharged from the nozzle and making it difficult to form a dense, homogeneous electron beam reflecting film. Moreover, a head (level difference) between the surface of the stored coating material and the nozzle changes as the coating material is spread over the shadow mask. This causes a change in pressure for supplying the coating material to the nozzle and therefore a change in quantity of the coating material discharged from the nozzle. This also causes uneven coating and makes it difficult to form a dense, homogeneous electron beam reflecting film.
Denser coating is needed for forming a surface coat over a glass panel surface by spraying, so that the surface coat can exhibit a low-reflection function and anti-static function. The conventional spraying method, however, tends to form an uneven film, and difficult to realize the surface coat exhibiting sufficient functions. The spin coating for surface coat has disadvantages such as low coating efficiency and high cost.
It is an object of the present invention to provide a method for forming a good electron tube by forming a dense, homogeneous electron beam reflecting film to control the doming phenomenon and thereby to solve the problems that cause deteriorated image quality. It is another object of the present invention to provide a method for forming a good electron tube by forming a dense, homogeneous electron beam reflecting film by spraying which presents high coating efficiency and is relatively low in cost.
The invention of claim 1 is a coating material dispersed with bismuth oxide, wherein an average particle diameter D50 of the bismuth oxide particles is 0.6 xcexcm or less, and particles having a diameter between D40 and D60 in a particle size distribution accounts for 20% or more in volume of the total particles. Because the particle size of bismuth oxide scatters little, a dense electron beam reflecting film with high surface coverage can be formed even with a small quantity by weight of the coating material.
The invention of claim 2 is a coating material dispersed with bismuth oxide using water as a solvent, wherein an average particle diameter D50 of the bismuth oxide particles is 0.6 xcexcm or less, and particles having a diameter between D40 and D60 in a particle size distribution accounts for 20% or more in volume of the total particles. For the same reason as described above, a dense electron beam reflecting film with high surface coverage can be formed even with a small quantity by weight of the coating material.
The invention of claim 3 is a coating material dispersed with bismuth oxide using water as a solvent and water glass as a binder, wherein an average particle diameter D50 of the bismuth oxide particles is 0.6 xcexcm or less, and particles having a diameter between D40 and D60 in a particle size distribution accounts for 20% or more in volume of the total particles. For the same reason as described above, a dense electron beam reflecting film with high surface coverage can be formed even with a small quantity by weight of the coating material.
The invention of claim 4 is a coating material dispersed with bismuth oxide using ethanol or methanol as a solvent, wherein an average particle diameter D50 of the bismuth oxide particles is 0.6 xcexcm or less, and particles having a diameter between D40 and D60 in a particle size distribution accounts for 20% or more in volume of the total particles. For the same reason as described above, a dense electron beam reflecting film with high surface coverage can be formed even with a small quantity by weight of the coating material.
The invention of claim 5 is a coating material dispersed with bismuth oxide using ethanol or methanol as a solvent and alcoholate of silica as a binder, wherein an average particle diameter D50 of the bismuth oxide particles is 0.6 xcexcm or less, and particles having a diameter between D40 and D60 in a particle size distribution accounts for 20% or more in volume of the total particles. For the same reason as described above, a dense electron beam reflecting film with high surface coverage can be formed even with a small quantity by weight of the coating material.
The invention of claim 6 is the coating material described in any one of claims 1 to 5, wherein the content of solids is 20% or less. With this, a dense electron beam reflecting film with high surface coverage can be formed without causing clogging of openings or liquid dripping.
The invention of claim 7 is an electron tube having a shadow mask of which plane to be irradiated with electron beams is coated with the coating material according to any one of claims 1 to 6. With this, high-quality images can be presented because the dense electron beam reflecting film with high surface coverage can be formed to exhibit a sufficient doming-control effect even with a small quantity by weight of the coating material.
The invention of claim 8 is an electron tube having shadow mask of which plane to be irradiate with electron beams is coated with no more than 0.2 mg/cm2 by weight of the coating material according to any one of claims 1 to 6. With this, high-quality images can be presented because the dense electron beam reflecting film with high surface coverage can be formed to exhibit a sufficient doming-control effect even with a small quantity by weight of the coating material.
The invention of claim 9 is an electron tube having shadow mask which is coated with the coating material according to any one of claims 1 to 6 in order to form thereon an electron beam reflecting film having a surface coverage of 40% or more. With this, high-quality images can be presented because the dense electron beam reflecting film with high surface coverage can be formed to exhibit a sufficient doming-control effect even with a small quantity by weight of the coating material.
The invention of claim 10 is an electron tube having a shadow mask of which plane to be irradiated with electron beams is coated with the coating material according to any one of claims 1 to 6 after dispersing the coating material by an agitator operating at a circumferential velocity of 30 m/s or more. With this, high-quality images can be presented because the dense electron beam reflecting film with high surface coverage can be formed to exhibit a sufficient doming-control effect even with a small quantity by weight of the coating material.
The invention of claim 11 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, characterized in that the coating material is supplied to the nozzle by means of a piezoelectric pump utilizing oscillations of a piezoelectric element provided therein. This method realizes stable coating by supplying the coating material to the nozzle by a precise, fine oscillations of the piezoelectric element, thereby causing little pulsation of the coating material being discharged.
The invention of claim 12 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein a piezoelectric element is actuated at an oscillation frequency of 20 Hz or more, and thus generated oscillations are utilized to supply the coating material to the nozzle. Utilization of high-frequency oscillations of the piezoelectric element allows control of fluctuations of pressure for supplying the coating material and stable discharge of the coating material from the nozzle.
The invention of claim 13 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein the coating is effected by slanting the nozzle at varying angles without varying a head (level difference) between the surface of the coating material in a coating material storage section and the nozzle center. When a large area is to be coated, keeping the head constant makes it possible to keep constant the pressure for supplying the coating material to the nozzle, and to stably discharge the coating material from the nozzle, thereby minimizing the scatter of the coated material by weight.
The invention of claim 14 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein the coating material is supplied to the nozzle by a piezoelectric pump utilizing oscillations of a piezoelectric element, wherein the coating is effected by slanting the nozzle at varying angles without varying a head (level difference) between the surface of the coating material in a coating material storage section and the nozzle center. Accurate supply of the coating material by means of the piezoelectric element secures a stabled discharge quantity of the coating material from the nozzle. In addition, when a large area is to be coated, keeping the head constant makes it possible to keep constant the pressure for supplying the coating material to the nozzle, and to stably discharge the coating material from the nozzle, thereby minimizing the scatter of the coated material by weight.
The invention of claim 15 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein a piezoelectric pump and the nozzle are assembled integratedly such that the center level of the piezoelectric pump becomes identical with that of the nozzle, and the coating is effected by simply scanning the nozzle without varying the positional relation between the piezoelectric pump and the nozzle. This method realizes stable discharge of the coating material from the nozzle by controlling fluctuations of pressure for supplying the coating material, said fluctuations being caused by changes in distance or positional relation between the nozzle and piezoelectric pump, so that the coating material can be accurately supplied to the nozzle.
The invention of claim 16 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein the coating is effected (a) by slanting the nozzle at varying angles without varying a head (level difference) between the surface of the coating material in a coating material storage section and the nozzle center by scanning the nozzle only in the horizontal direction in parallel to the plane, or by (b) slanting the nozzle while supplying the coating material to the nozzle by a piezoelectric pump, or by (c) integratedly assembling the piezoelectric pump and the nozzle such that the centers of the piezoelectric pump and the nozzle become identical in order to scan the nozzle without varying the positional relation between the two, thereby slanting the nozzle while supplying the coating material to the nozzle by the piezoelectric pump without varying the head between the surface of the coating material in the coating material storage section and the nozzle center. As a result, precise coating can be realized because the coating material can be accurately supplied to the nozzle and the discharge of the coating material from the nozzle can be stabled by controlling fluctuations of pressure for supplying the coating material to the nozzle that may be caused by vertical motion of the nozzle.
The invention of claim 17 is a coating method employing a device having a nozzle disposed to face a to-be-coated plane so that a coating material is coated over the plane by scanning the nozzle, wherein the coating material is supplied to the nozzle by a piezoelectric element operating at a frequency of at least 20 Hz, while controlling pressure of the coating material supplied to the nozzle by opening of a precision valve installed in a coating material recycling line, or wherein the nozzle is scanned only in the horizontal direction in parallel to the plane, while it is slanted at varying angles without varying a head between the surface of the coating material in the coating material storage section and the nozzle center, or wherein the coating material is supplied to the nozzle by a piezoelectric pump, while the nozzle is slanted at varying angles without varying the head between the surface of the coating material in the coating material storage section and the nozzle center, or wherein the coating material is supplied to the nozzle by a piezoelectric pump, while the nozzle is slanted at varying angles without varying the head between the surface of the coating material in the coating material storage section and the nozzle center, thereby keeping a constant positional relation between the piezoelectric pump and the nozzle by integratedly assembling them such that the centers of the piezoelectric pump and the nozzle become identical. As a result, precise coating can be realized because the coating material can be accurately supplied to the nozzle and the discharge of the coating material from the nozzle can be stabled by precise control, without being affected by pump flow characteristics and the like.
The invention of claim 18 is the coating method according to any one of claims 11 to 17, wherein the nozzle is a spray nozzle. This spray method realizes precise control of pressure for supplying the coating material to the spray nozzle without being affected by pump flow characteristics and the like, thereby enabling stabled discharge of the coating material from the nozzle.
The invention of claim 19 provides a method for producing an electron tube having a shadow mask, characterized in that the shadow mask is coated with a coating material for foring an electron beam reflecting film over the shadow mask by any one of the methods described in claims 11 to 18. This method enables it to form dense, homogeneous electron beam reflecting films by precisely supplying the coating material to the nozzle while controlling fluctuations of pressure for supplying the coating material to the nozzle, thereby securing high-quality images.
The invention of claim 20 provides a method for producing an electron tube by spreading a surface coating material over the surface of a glass panel in the electron tube by one of the methods described in claims 11 to 18. This method realizes dense and homogeneous coating by precisely supplying the coating material to the nozzle while controlling fluctuations of pressure for supplying the coating material, so that a high low-reflection function or antistatic function can be imparted to the coated surface film.